Promotion of peripheral nerve regeneration across large gaps continues to be substantial medical and engineering challenge. Materials with gradients of growth factors and adhesion factors have proven to be effective in enhancing nerve regeneration. However, these materials are still inferior to the gold standard, nerve autograft. The co-PI team of Elbert and Sakiyama- Elbert are leading an effort to produce synthetic materials that are superior to naturally derived regeneration matrices. The synthetic materials will be based on poly(ethylene glycol) (PEG) but will have many of the properties of fibrin. Most importantly, the PEG materials will have the novel ability to self-assemble gradients of growth factors and adhesion factors. The Elbert lab recently introduced a method of modular or 'bottom-up' scaffold assembly that uses PEG microspheres with different properties to assemble scaffolds in the presence of cells. One of the properties that can be easily modified is the buoyancy of the microspheres. Batches of microspheres with different buoyancies will self-assemble into a graded material upon centrifugation. This property will be used to establish gradients of the growth factor GDNF and the adhesion protein laminin in small scaffolds that are used for nerve guidance conduits. Although many techniques for gradient assembly are known, current methods become very challenging in small diameter conduits. The new method should prove to be more reliable and robust for generating growth factor gradients. The scaffolds will be engineered and evaluated in vitro in this project period in preparation for in vivo evaluation in subsequent project periods.